Storage disks are utilized in the computer industry, as well as other ever-expanding applications, for storage of information. Storage disks may be made of metal or glass and are subjected to a number of processing steps. Such storage disks must be transported, not only within the place of manufacturing during processing, but from the processing and manufacturing facilities to the manufacturing facility where the disks are placed in end use devices, such as disk drives. The disks are typically transported in plastic containers adapted for providing a generally sealed enclosure along with protection of the disks. It is critical for the disks that the enclosure be very clean and preclude entry of particles or other containments. Particles or other containments in the containers can adhere to the disks causing damage or necessitating additional cleaning steps.
Containers for storage disks have become generally standardized in their configuration as shown in Prior Art FIGS. 1–8. Such disk storage containers have three principal parts, a main body or cassette 20, a top cover 22 and a bottom cover 24. These component parts are generally molded from thermoplastic materials such as polycarbonate, polypropylene and the like.
The cassette is generally boxed shaped with an open top 26, an open bottom 28, a plurality of slots 30 typically formed by inwardly projecting ribs 32 disposed on the side walls 34 hold the disks in an axial arrangement. U-shaped openings or recesses 36 extend downwardly from the top edge 38 into the end walls 40 allow axial access to the disk apertures. The top covers generally have rectangular top portion 42 and two end portions 44 which extend downwardly from the top portion. The end portions close the openings 36 in the end walls 40.
Different means have been utilized to latch the top cover 22 to the cassette 20. One such latching means is shown in the Prior Art FIGS. 1 and 2 and is disclosed in U.S. Pat. No. 4,557,382. This embodiment utilizes end portions 44 that extend slightly inward to create an interference fit with the cassette. The end portions 44 must be flexed or deformed outwardly for the top cover 22 to be lowered and close the cassette. The top cover is then held in place by the inward bias or spring action of the end portions 44 and also by a frictional engagement between the catch edge 48 of the end portion 44 and a complementary locking catch 50 on the end wall 40 of the cassette 20. One potential disadvantage of the top cover latching mechanism of FIGS. 1 and 2 is that the inward bias of ends 44 can diminish or lessen outwardly over time such that the spring action or inward bias is reduced or, perhaps, lost. Additionally, some level of finesse is required to lower the top cover onto the cassette without making scrapping contact between the end portions 44 and any disks in the cassette or with the locking catch 50 of the end walls, which contact can generate contaminants. Additionally, there have been concerns that the engagement between catch edge 48, lip 49 and the locking catch 50 does not create a secure latch or an adequate seal, particularly around the entire length of the opening 36 in the end wall.
A second Prior Art reference is illustrated in FIGS. 3, 4, and 5 and is described in more detail in U.S. Pat. No. 5,253,755. This embodiment shows a disk container with a top cover 22 having an end portion 44 with a structural offset portion 54 shaped to snugly nest within the curvature of opening 36 formed by lip 56 of the U-shaped recess 36. This structural offset forms a seal with respect to the opening 36. In this Prior Art disk container, the top cover 22 is lowered down to the cassette and snaps into the engagement position as shown in FIG. 5. The ramped surface 58 engages the edge 56 of the opening as it is being lowered down and continued downward pressure on the top portion of the top cover urges the engagement member 60 outwardly to clear the edge 56 as shown in FIG. 5. Although this particular latching arrangement and top cover configuration has generally been accepted by the industry, concerns have been raised that such a snap-in top cover operates to launch particles from the top cover and cassette during the snap action. Said particles would thus be airborne and may end up as containments on the magnetic disks. Therefore it is desirable to have a latching mechanism that is not subject to the creep and sealing problems associated with the embodiment in FIGS. 1 and 2 and that also does not utilize the snap action of either of these embodiments.
A third Prior Art reference, U.S. Pat. No. 6,070,730, attempted to address the foregoing problems. This design is shown in FIGS. 6, 7 and 8. In this structure, like that disclosed in FIGS. 3–5, the top cover 22 includes end portions 44 having a structural offset portion 54 that rests within the opening 36 of the end wall of the cassette. However, the end portion 44 of the top cover 22 further includes an integral extension 62, disposed below the offset portion, and connected to the end portion by a hinge element 64. The locking members comprise a ramped surface 58 and engagement ledge 60 formed on the inside of the integral extension 62. The engagement ledge 60 is secured by opposed locking ledge 66 formed on the end wall 44 of the cassette 20. In this manner, the locking members 60 and 66 are physically separated from the structure 54 that closes the U-shaped opening 36. Also, there is no spring action or inward bias of the end portion 44 that causes particles to be projected into the container. Rather, the extension 62 must be affirmatively pressed inwardly to create engagement between engagement ledge 60 and locking ledge 66. Ramp 58 provides assistance if the cover is not squarely seated on the cassette. However, such affirmative action on the part of the operator is one draw back of the design. It is possible that the operator may not cause the integral extension 62 to fully engage the locking members, thereby creating the possibility that the cover would not be secure or could be unintentionally removed from the cassette leading to contamination of the contents. In addition, with repeated use, the hinge may weaken and tear or the locking members 60 and 66 may wear away, thereby diminishing their locking ability. This would render the container unuseable.